1. Field of the Invention
The present invention relates to a lead plate-attached coin-type battery whose lead plate is attached to exclusively either an outer can or a cap that covers an aperture of the outer can.
2. Description of the Related Art
Lithium secondary batteries are small, lightweight, and have a high energy density as well as superior storage characteristics (self-discharge characteristics). For these reasons, lithium secondary batteries have conventionally been widely used as a main power source or backup power source in various electronic devices. The lithium secondary batteries incorporated in such devices are coin-type, cylindrical-type, or the like, and mounting is widely performed by direct mounting to a printed board or the like.
The method for mounting a lithium secondary battery to a circuit board involves, for example, attaching one end of a lead plate (made of metal) to an external terminal face of the lithium secondary battery by spot welding, laser welding, or the like, inserting the other end of the lead plate into the terminal hole provided in the circuit board, placing and holding the lithium secondary battery onto a conductive land of the circuit board, and performing attachment by soldering.
The so-called solder reflow method is used to inexpensively mount electronic components to the circuit board. The solder reflow method involves applying cream solder to the conductive land of the circuit board, placing an electronic component on the face of the conductive land to which the cream solder has been applied, and then passing the entire circuit board through a reflow oven to perform heating thereof, thereby melting the cream solder and mounting the electronic component to the circuit board. Automatic soldering technology using the solder reflow method is also applied to the mounting of lithium secondary batteries to circuit boards.
When mounting the lithium secondary battery to the circuit board by the solder reflow method, the cream solder is melted by heating in a reflow oven at a high temperature of 230[° C.] to 270[° C.] for a short period of time. For example, when mounting a coin-type battery to a circuit board, first a positive lead plate is attached to the outer can, which is the positive terminal, and a negative lead plate is attached to the negative cap, which is the negative terminal. Next, the coin-type battery is mounted to the circuit board by soldering the positive lead plate and negative lead plate onto conductive lands on the circuit board by the above-described solder reflow method.
In recent years, in order to reduce the space occupied by mounting a coin-type battery to a circuit board, there has been proposed a method of omitting either the positive lead plate or negative lead plate, and directly soldering either the outer can or negative cap, whichever lacks a lead plate, to the conductive land of the circuit board (Japanese Patent Application Publication No. 2002-298804).
In the mounting method proposed in the aforementioned document, one of the lead plates is omitted when mounting the coin-type battery to the circuit board, thereby enabling reducing the mounted height of the coin-type-battery on the circuit board by the thickness of the omitted lead plate, which is not possible when lead plates are attached to both the outer can and the negative cap in mounting. Therefore, when using the method proposed in the aforementioned document, it is possible to reduce the space occupied by the coin-type battery on the circuit board or increase the thickness of the coin-type battery by the thickness of a lead plate. If the thickness of the coin-type battery is increased, a higher capacity coin-type battery can be mounted in the same amount of occupied space.
However, when using the mounting method proposed in the aforementioned document, there are cases in which the strength of the bond between the coin-type battery and the conductive land on the circuit board is insufficient, and detachment can occur in the bonded portion by vibrations to the circuit board on which the coin-type battery has been mounted. Also, there are cases in which cream solder that has melted during reflowing flows out beyond the conductive lands, thereby causing short circuits with the other pole of the coin-type battery and other conductive lands on the circuit board.